Preparation of benzene hexachloride



United States PatentC PREPARATION OF BENZENE HEXACHLORIDE Frederick E. Kung, Akron, Ohio, assignor to Columbia- Southern Chemical Corporation, Allegheny County, Pa., a corporation of Delaware No Drawing. Application August 13, 152, Serial No. 304,230

2 Claims. (Cl. 260-648) This invention relates to a novel method of producing benzene hexachloride by addition chlorination of benzene.

It is known that chlorine may be reacted with benzene in the absence of a substitution catalyst under conditions which promote addition chlorination to prepare benzene hexachloride. In general, the processes described in the literature which have been proposed or used to chlorinate benzene and produce benzene hexachloride have employed actinic light, such as ultraviolet, to activate the reaction.

At least five isomeric forms of benzene hexachloride are produced by known addition chlorination processes. These isomers have been designated as alpha, beta, gamma, delta and epsilon isomers. For particular purposes, such as in the insecticidal field, it is conventionally recognized that a high gamma isomer content is desirable. Accordingly, one of the particular objectives has been to achieve high gamma isomer concentrations in the 1 reaction product.

Gamma isomer contents consistently in excess of those produced by conventional processes may be attained by resort to specific reaction conditions. For example, gamma isomer contents consistently from 19 to 20 per cent by weight, and frequently from 24 to 28 per cent by weight, may be achieved by adding chlorine to a liquid reaction mixture of benzene and a partially halogenated hydrocarbon irradiated with actinic light while maintaining a substantial chlorine concentration not in excess of 1.5 per cent by weight of the benzene and partially halogenated hydrocarbon at a reaction temperature below the freezing point of benzene but at which the reaction mixture is liquid. These gamma isomer contents are considerably greater than the 12 to 16 per cent concentrations achieved by practice of the conventional processes described in the literature.

One of the critical reaction conditions in the aforedescribed high gamma photochlorination process is the chlorine concentration in the reaction mixture which must be above 0.005 per cent but not in excess of 1.5 per cent by weight of the benzene and partially halogenated hydrocarbon. Control of this chlorine concentration is provided by correlating the rate at which chlorine is added to the reaction mixture and the rate at which chlorine reacts with benzene. The rate of reaction for formation of benzene hexachloride is proportional to the intensity of the actinic irradiation. Thus, chlorine concentration control in such a process entails balancing the chlorine addition rate with the activating influence of the irradiation.

The catalytic effect of actinic irradiation during the course of the reaction varies considerably. For example, it has been observed that the rate at which chlorine reacts with benzene to form benzene hexachloride continuali ly diminishes as the reaction proceeds. Accordingly, unless the rate of chlorine introduction is decreased and/ or the intensity of the actinic irradiation is increased, the concentration of chlorine in the reaction mixture builds up to a level which is outside of the range for optimum gamma isomer concentration in the aforedescribed method of preparing benzene hexachloride.

Expedients which may compensate for the decreasing efiiciency of the irradiation are not altogether satisfactory. It is possible, for instance, to reduce the rate at which chlorine is added to the reaction mixture. This, of course,-

appreciably lengthens the reaction period per ton of product. More equipment per ton of product is therefore required. increasing the intensity of the irradiation is also possible. However, to attain the desired high gamma isomer contents, reaction temperatures of from about 5 C. (freezing point of benzene) to as low as minus C. are required. Maintaining these low temperatures when more intense irradiation is employed requires increased refrigeration. In large scale operations, the uniform removal of sufiicient heat tomaintain accurate temperature control requires specially designed equipment. Further increasing the refrigeration load, is therefore undesirable, and frequently a limiting factor in production.

According to this invention, a novel process is provided which is simple-to perform and which does not require actinic light. It has been found that addition chlorination of benzene may be performed by carrying out the reaction in the presence of trichloroaceyl peroxide. The use of this catalyst is of particular value in the aforedescribed low'temperature process because, unlike actinic irradiation, the catalytic eitect of the trichloroacetyl peroxide present in the reaction mixtureis not dependent on the degree of benzene conversion that has already taken place. That is, a given amount of trichloroacetyl peroxide is equally eifective as a catalyst at any time during the course of the reaction. Thus, practice of this invention circumvents the aforedescrib'ecl disadvantages of photochlorination processes.

This invention may be practiced by recourse to various procedures. For instance, chlorine may be added to a reaction mixture of benzene and a partially halogenated hydrocarbon, such as methylene chloride, containing a catalytic amount of trichloroacetyl peroxide while maintaining the reaction temperature below 5 C. and above the freezing point of the reaction mixture and maintaining the chlorine concentration between 0.005 to 1.5 per cent by weight of the-benzene and partially halogenated hydrocarbon. Once the chlorine addition rate is balanced with the reactionrat'e, the chlorine concentrationis established and the trichloroacetyl peroxide concentration is maintained, the reaction will proceed at a relatively constant rate until essentially all of the benzene has been converted to the product. I

It may therefore be noted, for example, that-trichloroactyl peroxide provides the benefits described hereinbefore in the process of preparing benzene hexachloride wherein chlorine is added to a reaction mixture of benzene and a solvent other than a partially halogenated solvent, at temperatures below the freezing point of benzene wherein the chlorine concentration is maintained between 0.005 and 2.0 per cent by weight of the benzene and solvent. Typical solvents include fluorochloromethanes such as dichlorodifluoromethane, trichloromonofluoromethane, and higher fully fiuorinated and chlorinated hydrocarbons containing only fluorine, chlorine and carbon atoms. Fully halogenated hydrocarbons including carbon tetrachloride, carbon 'tetrafiuoride and the like which are liquid at the reaction temperature may likewise be employed. Other liquids such as liquid sulphur dioxide, liquid sulphuryl chloride, liquid phosgene', kerosene, thionyl chloride, propionic anhydride and like liquids are also useful. As a general rule, any solvent which is liquid at reaction temperature and which is essentially inert at reaction conditions may be employed. Even those solvents which only chlorinate slightly or which, upon chlorination yield commercially useful'products, may be employed.

Trichloroacetyl peroxide will catalyze the addition chlorination of benzene under conditions other than those previously described. It maybeemployed in lieu of-actinic light, or other recognized catalysts, to promote this reaction, in any of the known benzeneaddition chlorination processes employed in 'thepreparation of benzene hexachloride. However, as already explained, it provides particular advantages over catalytic agents suchas actinic light when employed in processes requiring particularly low reaction temperatures and accurate control of chlorine concentrations in the reactionmixture.

It is emphasized, however, that not all organic peroxides are suitable in the practice of processes which require chlorination at temperatures below C. At these low temperatures, most organic peroxides have little or ,no catalytic properties in addition chlorination of benzene. Thus, benzoyl peroxide, for example, is an inefiective catalyst at temperatures below .5"C. Accordingly, trichloroacetyl peroxide catalysis also provides advantages over the use of other peroxides, such as benzoyl peroxide since it is capable of promoting addition chlorination of benzene at temperatures below 5 C.

The amount of trichloroacetyl peroxide which is. required to catalyze this low temperature reaction is quite small. In fact, even traces will catalyze the reaction. For most purposes, from 0.1 to about 5 to per cent by weight of trichloroacetyl peroxide, based on the benzene and partially halogenated hydrocarbon, is suitable. Larger amounts do not appear objectionable. The most suitable amount of trichloroacetyl peroxide is related to the rate of reaction and particular reaction temperature. At a given temperature, the rate of reaction may be increased by employing larger amounts of trichloroacetyl peroxide. Similarly, if the reaction temperature is lowered, increased amounts of trichloroacetyl peroxide are required to maintain the same reaction rate.

Suitable control of chlorine concentrations is achieved by balancing the catalytic effect of trichloroacetyl peroxide with the rate of chlorine addition for each temperature. When higher addition rates are desired, an appropriately .increased amount of trichloroacetyl peroxide, which provides a reaction rate corresponding to the higher addition rate, is employed.

The partially halogenated hydrocarbons which are conducive to the production of high gamma isomer contents in this invention are those having from 1 to 4 carbon atoms. Particularly good results may be obtained by using partially chlorinated aliphatic hydrocarbons containing 1 or 2 carbon atoms, such as methylenechloride, methyl chloride, chloroform, methyl chloroform, and ethylene dichloride. However, othercompounds, such as l,l',2-trichloroethane, tertiary butyl. chloride, secondary butyl chloride, isopropyl chloride, ,isobutyl chloride, n-propyl chloride, l,1,2,2,3-pentachloropropane, higher butane halides, etc., containing up .to and including 4 carbon atoms, and analogous bromides, iodides or fluorides may be employed.

The amount of partially halogenated hydrocarbon which is employed with benzene may be varied from 5 or 10 to 99 per cent by weight of the benzene and partially halogenated hydrocarbon. In general, highest gamma isomer contents are attained .whenlhigher concentrations of the partially halogenated hydrocarbon are used,:for example, when 30 to95. per cent by weight of the hydrocarbon is employed.

Reaction temperatures below 5 C. and above the freezing point of the reaction. mixture may normally be employed. Preferably, the reaction is carried out between 5 ,C. and minus C. or even minus C. Lower temperatures have certain ..advantages, such as high gamma contents, but require larger amounts ofcatalyst and added refrigeration. .Thus, ,in.-prac,tice, these factors are balanced in selectingthe, actual operatingtemperature.

As has been previously pointed out, the chlorine concentration must be maintained between, 0.005 and 1.5 per cent by weight of the benzene and partially halogenated --in this-range varies'with the reaction temperature, the partially halogenated hydrocarbon used, and the relative proportions of benzene and partially halogenated hydrocarbon present in the reaction mixture.

It is preferable to exercise certain precautions in order to obtain best results in the practice of this invention. The; presence of elemental oxygen-in the reaction-mixture is undesirable. It is therefore advantageous to flush the system with essentially pure nitrogen prior to and during the course of the reaction; Essentially pure reactants should be used. For example, benzene may be partially photochlorinated and then distilled with the ends discarded in order to remove impurities. Also, since trichloro acetyl peroxide decomposes readily at room temperature, it should be freshly prepared or be stored at sub-zero temperatures, such as minus 30 0, prior to use. Of course, the presence of materials favoring substitution chlorination of benzene in the reaction system should be avoided.

Although the invention has been described with reference to the use of trichloro acetyl peroxide per se, it may be practiced by employing trichl oro acetyl peroxide in conjunction with other known catalysts which are operable at temperatures below the freezing point of benzene. Thus, trichloroacetyl peroxide in combination with actinic light, or gamma irradiation or other high frequency electromagnetic radiation, or peroxydicarbonate esters such as isopropyl peroxydicarbonate may'be used.

Thefollowing example illustrates the practice of this invention:

Example I -6 centimeters. ,A rubber stopper closed the opening in one verticalarm. Near the top of this verticalan openingwasprovided leading to a dry ice condenser for condensing low boiling halogenated hydrocarbons, and the condenser .was connected to suitable traps for collecting any. HCl driven off during the reaction. A thermometer was inserted in this arm through the stopper to measure thetemperature of the reaction mixture. A- high speed propeller, driven bya suitable motor, was inserted into the other vertical armthrough the opening in the top thereof to circulate the reaction mixture. Introduction of chlorine and nitrogen Was provided near the top of this vertical arm, and a stop cock for removal of the product for chlorine analysis was provided nearthe bottom. of this vertical arm.

The entire apparatus was shielded from light by a light impermeable coating. The lower portion of the circulatory-apparatus was placed in a container containing a dry ice-acetone mixture suitable for cooling of the reaction mixture.

Priorto the reactions, benzene and methylene chloride were specially purified. The benzene was partially photochlorinated toremove small amounts of easily chlori- -natable impurities and then distilled, while the methylene chloride was distilled through a l5-plate column to remove any inhibitory materials.

A solution of 335 milliliters of methylene chloride and 200 milliliters of benzene was placed in the reactor. Circulation and cooling was then. started and when the temperature fell below the reaction temperatureof the run,.the trichloroacetyl peroxide was added to the charge in the amounts indicated in the table. The apparatus was. flushed with nitrogen for 30 to 60 minutes.

Gaseous chlorine at the rate indicated in the table and 0 mm m mam e V wm m m e a m v. n 0 w b Pw s e f m 5 e wa a ew o w sm s m mm m o u m h a r. U m m .6W6 nm l mms llonnu w mm se m Omm m I ,3 OOH 11 8 t mn n a CH. rda m ee n mk emm n me 3 0 f. nu flv. ednab g ut O De mo m 8d The What is claimed:

1. In a process of preparing benzene hexachloride by addition chlorination of benzene at temperatures below the freezing point of benzene, the improvement which comprises carrying out the reaction in the presence of trichloroacetyl 1 peroxide. I

2. In a method of preparing benzene hexachloride by adding chlorine to a mixture at a temperature below the freezing point of benzene containing benzene wherein the 15 chlorine concentration in the mixture is maintained besodium thiosulfate. ulated to find per the sample for all 10 ction conditions Average Chlorine Concentration. Percent 0 O O Q0 D 0 0 0 0 0 0 O 0 0 0 Table Addition, Grams 0 9M225 0 0 O 0 QZ0 0 0 O 0 g potassium iodide solution. was thus obtained, and the liberated Tri-chloro Chlorine Acetyl Peroxide, Percent by QQQQQQQQQQQQQQQO Temperature, C.

The following table summarizes the rea and results:

Run

tared flask containin weight of the sample iodine was titrated with 0.01 to 0.1 N The concentration of chlorine was calc cent by weight of chlorine present in 1 experiments. 1 f

1 The temperature could not be held constant when 5.3 grams per mire 35 ute of chlorine was added but varied between 0 and 5 C. 

1. IN A PROCESS OF PREPARING BENZENE HEXACHLORIDE BY ADDITION CHLORINATION OF BENZENE AT TEMPERATURES BELOW THE FREEZING POINT OF BENZENE, THE IMPROVEMENT WHICH COMPRISES CARRYING OUT THE REACTION IN THE PRESENCE OF TRICHLOROACETYL PEROXIDE. 